Atrial Fibrillation
Cardiac arrhythmias, and atrial fibrillation in particular, remain a persistent medical condition in modern society. In the United States alone, approximately 1% of the total adult population is afflicted by atrial fibrillation, currently more than 2.5 million people, with prevalence increasing as a function of age. The resulting loss of blood flow due to incomplete cardiac contractions along with a rapid heart rate can lead to shortness of breath, dizziness, limited physical endurance, and chest pains. Persistence of atrial fibrillation renders an individual susceptible to congestive heart failure, stroke, other thromboembolic events, and myocardial ischemia. Considerable information is evolving regarding the conditions of the heart which contribute to the appearance of atrial fibrillation, factors which may be exacerbated by stress, anxiety, high blood pressure, heart valve disorders, and heart muscle dysfunction. An initial overview of the clinical phenomena associated with atrial arrhythmia is as follows.
The mammalian heart is composed of three different categories of cardiac tissue namely, atrial, ventricular, and excitatory conduction types. Normally, the atrial and ventricular muscles of the heart are electrically excited in a synchronous, patterned fashion. The cardiac cycle commences with the generation of action potentials by the sino-atrial (SA) node, located in the lateral wall of the right atrium. These action potentials propagate through the atrial chamber, possibly along preferential conduction pathways leading to the atrioventricular (AV) node. Potentials emanating from the AV node travel through the His-Purkinje bundle to the ventricular tissue, causing a synchronous contraction of the ventricles following that of the atria.
Pathological conditions of the cardiac tissue may lead to asynchronous cardiac rhythms, resulting in an overall elevation in the heart rate, inclusive of paroxysmal or clironic tachycardias. Tachycardias may initiate in the AV node, the bundle of His, or more generally in the atrial or ventricular tissues. The aforementioned tachycardias may manifest as a multiwavelet reentrant mechanism, resulting in asynchronous eddies of electrical impulses scattered about the atrial chamber. The fibrillation may also be more focal in nature, caused by the rapid, repetitive firing of an isolated center within the atria, but so rapidly that the remainder of the atrium cannot follow in a synchronized fashion.
Presently, many categories of tachycardia may be detected using the electrocardiogram (EKG). An alternative, more sensitive procedure commonly used to detect localized aberrations in electrical activity, and thus confirm the presence of arrhythmias such as atrial fibrillation, is the mapping of the cardiac chambers as disclosed in U.S. Pat. Nos. 4,641,649 and 4,699,147 and WO 96/32897.
Numerous cardiac arrhythmias, such as atrial fibrillation, were once thought untreatable except by pharmacological or surgical intervention, both capable of manifesting undesirable side effects. Recently, the emergence of less invasive catheter ablation methods have expanded the field of cardiac electrophysiology to provide limited percutaneous solutions to the medical conditions just described. A brief description of the aforementioned conventional therapies for atrial fibrillation and approaches to cardiac ablation thereof is found below.
Regimes of Conventional Treatment
Episodes of tachycardia may be responsive to treatment by antiarrhythmic medication, as disclosed in U.S. Pat. No. 4,673,563 to Berne et al. and further described in U.S. Pat. No. 4,569,801. In addition, pharmacological intervention for treating atrial arrhythmias has been disclosed in the Hindricks, et al. in "Current Management of Arrhythmias" (1991). However, the administration of such medications sometimes does not restore normal cardiac hemodynamics, and may ultimately exacerbate the arrhythmic condition through the occurrence of proarrhythmia.
Specific clinical circumstances may necessitate invasive surgical intervention for multiwavelet tachycardias, including the placement of implantable atrial defibrillators to maintain sinus rhythms as disclosed in U.S. Pat. Nos. 4,316,472; 5,209,229; 5,411,524 or alternatively, by the mechanical destruction of atrial electrical conduction pathways, as described by Cox, JL, et al. in "The surgical treatment of atrial fibrillation. I. Summary" Thoracic and Cardiovascular Surgery 101(3), pp. 402-405 (1991) or Cox, JL "The surgical treatment of atrial fibrillation. IV. Surgical Technique", Thoracic and Cardiovascular Surgery 101(4), pp. 584-592 (1991).
Described by the Cox procedure, as referenced above, is a strategy to incur patterned surgical incisions within the atrial chambers, creating a maze by which propagating electrical waves are extinguished at the lines of suture. In this way, reentrant wavelets are not sustained, arrhythmia cannot persist, and normal sinus rhythm is restored. Curative efforts for atrial arrhythmias were initially focused on the right atrium, with mixed results. However, procedures which combine right and left atrial treatments have been observed to have dramatically increased success rates. In the left atrium, a common protocol includes vertical incisions from the two superior pulmonary veins and terminating just posterior to the mitral valve annulus, transversing the inferior pulmonary veins en route. An additional horizontal line also connects the superior ends of the two vertical incisions. Thus, the region of the pulmonary vein ostia is isolated from the other atrial tissue. By severing electrical conduction pathways within the atrial tissues, the fibrillatory process is eliminated.
Transcatheter Cardiac Ablation
Alternative, less invasive approaches have recently been adopted for the treatment of cardiac arrhythmias in a clinical setting. These catheter-based transvascular approaches include procedures and associated devices for the treatment of ventricular or supraventricular tachycardias, as described in Lesh, MD in "Interventional Electrophysiology - State of the Art, 1993" American Heart Journal, 126, pp. 686-698 (1993).
The initial approach to the ablative procedure used catheters responsive to high energy direct current (DC) to either disrupt the AV node function or to create a heart block by disruption of the His bundle. However, it has been more recently observed that radio frequency (RF) is often a more desirable energy source as disclosed in WO 93/20770. Alternative ablation techniques have also been disclosed. For example, an ablative catheter responsive to microwave frequencies is described in WO 93/20767. Other catheter based ablation technologies which have also been disclosed to render the aberrant cells electrically silent include freezing, ultrasound, and laser energy as disclosed in U.S. Pat. Nos. 5,147,355; 5,156,157 and 5,104,393, respectively.
Ablation procedures have typically involved the incremental application of electrical energy to the endocardium to form focal lesions to interrupt the inappropriate conduction pathways. Methods and devices for using percutaneous ablative techniques intended to remedy cardiac fibrillation or arrhythmias have been disclosed in U.S. Pat. Nos. 5,231,995; 5,487,385; WO 94/21165 and WO 96/10961 in addition to U.S. Pat. Nos. 5,228,442 and 5,324,284 to Imran. The disclosures of these references are herein incorporated in their entirety by reference thereto.
For some types of cardiac arrhythmias, a focal ablative lesion (i.e., 5-8 mm in diameter) is adequate to sever inappropriate conduction pathways such as those associated with the Wolff-Parkinson-White syndrome. owever, such focal lesions are not appropriate for most cases of atrial fibrillation which involve multiple reentrant loops. These excitation waves would simply go around a focal ablative lesion. Thus, as in the surgical "maze" procedure, long linear lesions are required in order to segment the atrium to block the wave fronts associated with most forms of atrial fibrillation.
Certain particular catheter based technologies exist which are intended to emulate all or a portion thereof, the incision patterns of the maze procedure using curvilinear catheters. The use of such catheters in ablative procedures is disclosed in Avitall et al., in "Physics and Engineering of Transcatheter Tissue Ablation", Journal of American College of Cardiology, Volume 22, No. 3:921-932 (1993). In addition, the use of transcatheter ablation to remedy atrial fibrillation in a clinical setting, specifically by the use of a percutaneously introduced ablation catheter (with either a 7F deflectable 4-mm tip with thermocoupler; Cordis Webster, Miami, Fla., or a woven Dacron 14 by 4-mm multielectrode from Bard Electrophysiology, Tewksbury, Mass. is described in Haissaguerre, et al. in "Right and Left Atrial Radiofrequency Catheter Therapy of Paroxysmal Atrial Fibrillation" in Journal of Cardiovascular Electrophysiology 7(12), pp. 1132-1144 (1996). These articles are herein incorporated in their entirety by reference thereto.
The aforementioned references disclose methods which use a sequential application of energy from a point on a catheter, which is remotely manipulated, to ostensibly create an ablation maze according to a predetermined pattern. However, this process may fail to produce continuous, transmural lesions, thus leaving the opportunity for the reentrant circuits to reappear. In addition, minimal means are available in these embodiments for steering the catheters to anatomic sites of interest such as the pulmonary veins.
Catheter Positioning Technology
Many different types of catheters have been disclosed for guiding, accessing, and positioning at a predetermined location within the body for the purposes of performing a medical treatment.
A number of steerable catheter systems, exhibiting a plurality of curvatures at their distal end, have been devised which may be introduced into the blood vasculature or other lumen, navigating the many passageways, ultimately reaching previously inaccessible areas within the cardiac chamber without invasive surgery. For example, catheters with complex curvatures and preshaped member loops have been devised for placement in the cardiac chambers as described in U.S. Pat. Nos. 4,117,836 (left coronary artery); 5,195,990 (aorta); the right ventricle in U.S. Pat. No. 4,882,777; U.S. Pat. No. 4,033,031 discloses a catheter design for access of the pericardial space. Additional examples of intravascular steerable catheters used in cardiac ablative procedures are disclosed in U.S. Pat. Nos. 4,898,591 and 5,231,994. The disclosures of these references are herein incorporated in their entirety by reference thereto.
One class of catheters exemplifies steerable guidewires as rails. Of these, 25 some are "over-the-wire" types of catheters which have lumens substantially extending along their entire length and which are adapted to track over a guidewire. Other "guidewire tracking"-types of catheters have also been disclosed, generally referred to "rapid-exchange" or "monorail" catheters, which have only a distal region of the catheter length adapted to track over a guidewire. This type of catheter benefits in the ability to separately control proximal regions of both the guidewire and also the catheter externally of the body, since only the distal region of the catheter is coaxial over the guidewire. Examples of these types of catheters are disclosed in U.S. Pat. Nos. 5,300,085 and 5,501,227 to Yock.
Furthermore, the use of particular guiding sheath designs for use in ablation procedures in both the right and/or left atrial chambers are disclosed in U.S. Pat. Nos. 5,427,119; 5,497,119; 5,564,440; 5,575,766 to Swartz et al. In particular, the aforementioned art describes a method which requires a real time repositioning of a point source of energy along a preferred pathway in the moving wall of a beating atrium. In doing so, a remote percutaneous manipulation of the device is required using only the means of X-ray fluoroscopy for visualizing catheter location. Moreover, the use of a monorail catheter with several deployable shapes for the purposes of creating incremental lesions along a predetermined linear path in the right atrium, accomplished by sustaining the elongate ablation element at a predetermined location along a body space wall, is disclosed in U.S. Pat. No. 5,487,385 to Avitall.
Several catheter designs have also incorporated a plurality of distally located mechanisms to stabilize the catheter, thus enabling precise placement of the ablation electrodes within a cardiac chamber. Such technologies may include the use of a stop and/or a balloon as disclosed in U.S. Pat. Nos. 5,487,385 and 5,496,346, respectively, along the guidewire contained in the catheter. Alternatively, a catheter adapted to be mechanically retained in a fixed position within a vessel lumen is disclosed in U.S. Pat. No. 5,509,500 to Kirkman. Furthermore, the positioning of a catheter within the heart using a distally located inflatable balloon device during ablation procedures has been disclosed in U.S. Pat. Nos. 5,571,159 to Alt and 4,762,129 to Bonzel.
None of the cited references discloses a tissue ablation device having an ablation element having anchors at each of two ends for anchoring the ends to first and second predetermined locations along a body space wall in order to secure the length of the ablation element to the tissue between those locations for ablating a long linear lesion.
None of the cited references discloses a kit of multiple ablation catheters, each having a unique ablation length which may be chosen for use in the formation of a long linear lesion between two anatomic anchoring points, such as the two pulmonary vein ostia, according to the measured length of the distance between those anatomic sites in a patient.
None of the cited references discloses a catheter having a means for selectively positioning an intermediate region of the catheter located proximally of the distal tip, nor do they disclose a catheter having a guidewire tracking region with both proximal and distal guidewire ports positioned on that intermediate catheter region.
In addition, none of the cited references discloses a catheter device that provides a multirail guidewire tracking capability at various positions along the catheter length.
Still further, none of the cited references discloses a tissue ablation device assembly having an elongate ablation element with at least one suctioning port along its length which is coupled to a suction source in order to anchor the ablation element to tissue along a body space wall.